The New Sudoku Players' Forum

[Cec]

Hi This is my first post. As a new player i share similar confusion as Janiv Ratson (joined 15 June) who was advised by George (joined 20 May)in explaining "disjoint subsets" to look at cells r2c2, r2c3 and r2c6 in the following row and work out what are the only three digits that can go in these three cells:
(9), (1,5,7), (5,7), (3), (2,8,7), (1,5), (4), (5,6,7), (1,2,6.8)
iIfail to see how the chosen three candidates 1,5 and 7 would only occupy the three cells r2c2, r2c3 and r2c6 when these same candidates also occur in columns 5,8 and 9. No offence but please don't advise me it should be obvious but please explain why.
Bonsai Cec

[simes]

With the candidates:
(9), (1,5,7), (5,7), (3), (2,8,7), (1,5), (4), (5,6,7), (1,2,6.8)


there are three cells that have ONLY 1, 5 and 7 as candidates between them. Three cells, with three possible candidates means that one of the candidates must occupy each cell - though we don't yet know which is which. (If you don't believe this, try allocating one of each candidate to each cell such that each digit is different - sort of a mini Sudoku with the other constraints removed.)

Since these three candidates are accounted for, they can be eliminated from the other cells, leaving
(9), (1,5,7), (5,7), (3), (2,8), (1,5), (4), (6), (2,6.8)

[scrose]

Another way to look at this. We start with the following.

[9] {157} {57} [3] {287} {15} [4] {567} {1268}

Ignoring the constraints of other columns and blocks, try putting a 7 in column 5, and thus remove the other 7's from the row.

[9] {15} {5} [3] [7] {15} [4] {56} {1268}

5 is the only candidate remaining in column 3, so remove the other 5's from the row.

[9] {1} [5] [3] [7] {1} [4] {6} {1268}

We are left with a contradiction of 1 being the only candidate remaining in each of two columns.

You will reach similar contradictions if you attempt to place a 5 or a 7 in column 8, or a 1 in column 9.

Thus, columns 2, 3, and 6 are the only columns in which the candidates 1, 5, and 7 can be.

[Animator]

What about these candidates:

(9), (1,5,7), (1,5,7), (3), (2,8,7), (1,5,7), (4), (5,6,7), (1,2,6.8)

Do you see now why those are the only three possible cells?

Also, have you looked at pairs (group of 2 numbers) and do you understand them fully? If you haven't then you should do that first.